Electrolytes for the electrodeposition of platinum



United States Patent 3,347,757 ELECTROLYTES FOR THE ELECTRGDEPOSITION 0F PLATINUM Roger Lacroix, Snresnes, and Charles Beclier, Paris, France, assignors to Comptoir Lyon-Alemand, Louyot & Cie, Paris, France N0 Drawing. Filed Feb. 11, 1964, Ser. No. 343,933 Claims priority, application France, Feb. 12, 1963, 924,431 10 Claims. (Cl. 204-47) The present invention relates to a process for the electrodeposition of either thin layers or relatively thick layers of platinum on the majority of non-ferrous metals such as gold, silver, nickel, copper and their alloys, and further relates to a new electroytic bath for the application of said process.

Existing formulae for electrolytic platinum-plating baths are both numerous and of very difierent types, but none has given entirely satisfactory results.

The oldest formula is based on the use as main constituent of the electrolyte platinum II diaminodinitrite which is also known as P salt. This complex salt which can be readily prepared and obtained in a high state of purity is dissolved at 95 C. in an ammonia solution. A certain quantity of ammonium nitrate ensures good conductivity of the electrolyte. This bath works at a high temperature of 95 to 100 C., which produces a constant variation in the ammonia concentration which requires constant readjustment. The deposits obtained rapidly become grey, black, powdery or spongy. Moreover, such a bath has a very low yield and can even become zero after a certain time of operation.

Another method consists in the use of an alkaline bath of sodium hexahydroxyplatinate Na Pt(OH) containing caustic soda and sodium sulphate. The deposits obtained are greyish and rapidly become powdery.

Other processes of more recent date are based on the use of chloroplatinic acid H PtCl or of complex salts such as potassium dinitroplatinate-sulphate K Pt (N0 80 These baths make it possible to deposit only very thin layers of platinum since the yield which is low at the outset decreases in the course of time.

The main object of the present invention is to make said processes such that they meet the various practical requirements more effectively than has hitherto been the case, especially insofar as they provide a remedy to the disadvantages of the process of the prior art which have been mentioned above and make it possible to obtain deposits of platinum which have relatively substantial thickness, are bright in appearance, are free from internal stresses, and have a high hardness number.

Another object of the invention is to obtain an electrolyte which does not have the defects of the prior art electrolytes particularly insofar as it is stable, has a constant action and a high rate of deposition as well as good covering power.

The process in accordance with the invention mainly consists in the electrolysis of a solution containing platinum II diaminodinitrite or P salt and fiuoborate ions BF, which is obtained by adding P ionic solution of heated fiuoborate in to 40 g./liter or more.

Aside from this main arrangement, the process in aca proportion of 5 cordance with the invention additionally consists in certain other arrangements which are preferably employed at the same time and which can be considered either separately or in combination, namely:

the addition of fiuoborate ions is supplied by fluoboric acid in a proportion of 0 to 100 g./liter,

salt to an aqueous,

the addition of fiuoborate ions is supplied by an alkaline fiuoborate in the proportion of 0 to 200 g./liter,

the alkaline fiuoborate is sodium fiuoborate, the alkaline fiuoborate is potassium fiuoborate,

the alkaline fiuoborate is ammonium fiuoborate,

the addition of fiuoborate ions is supplied by a mixture of fluoboric acid and alkaline fiuoborate within the limits of the proportions given above.

The invention finally consists of an electrolyte which is suitable for the electrodeposition of a platinum coating, characterized in that it is constituted by the aforesaid aqueous solution which is obtained by heating the platinum II diaminodinitrite in an aqueous solution containing fiuoborate ions.

Other objects and advantages of the invention will become apparent by consideration of the following complementary description and examples, it being understood that said complementary description and examples are given solely by way of indication and not in any sense by way of limitation.

The principal of the invention is based on the fact that platinum II diaminodinitrite dissolves in the hot state in aqueous solutions containing fiuoborate ions BF Said ions form with P salt a more stable complex than P salt itself. Consequently, by dissolving P salt in the hot state in a solution containing an alkaline fluoborate or fiuoboric acid or both at the same time, there is thus formed a stable electrolytic solution which makes it possible to deposit under the usual conditions of electrolysis thick layers of platinum which have a bright luster and are free from internal stresses.

The mode of preparation in accordance with the invention consists in starting with a solution containing from 5 to grams of fiuoboric acid per liter or from 20 to 200 grams of an alkaline fiuoborate or a mixture of both of these substances, in bringing to the boil and then in slowly introducing P salt in a proportion of 5 to 40 grams or more per liter.

The solution is allowed to boil for a few minutes While taking care to maintain the liquid at a constant level by addition of distilled water, the bath being ready to operate. Electrolytic layers of the majority of non-ferrous metals and alloys formed with copper, nickel, silver, gold, brass, bronze, nickel silver, etc. provided that the part to be coated is introduced under tension in the bath.

The characteristics of operation of a bath of this type are as follows:

Platinum II diaminodinitrite 5 to 40 g./liter or more. Sodium fiuoborate, potassi-.

um fiuoborate or ammonium fiuoborate 20 to 200 g./liter. Fluoboric acid 5 to 100 g./liter. Anodes Platinum.

Ratio of anode surface area to cathode surface area 1/1 or upwards.

Temperature of bath 40 to 100 C. pH value 0 to 5. Agitation Medium of anode and of cathode, or of bath. Weight of metal deposited per ampere-minute 10 to 20 mg.

The proportion of fiuoboric acid is indicated by weight of pure acid. If a high concentration of this acid is employed, it is not necessary to add sodium fiuoborate; the deposits obtained have a brighter luster but are then subject to internal stresses ata very substantial thickness.

The replacement of a proportion of fiuoboric acid by an alkaline fluoborate either reduces or completely eliminates stresses within the deposit.

The purpose of the alkaline fluoborate is to permit the P salt to dissolve as a result of the formation of a stable complex and to provide the bath with good conductivity. The addition of a small quantity of free fluoboric acid so as to reach a pH value of 1 to 2 makes it possible to increase the rate of deposition and makes the deposit brighter in appearance.

The electrolytic process can be carried out in glass vessels when baths are employed which have a low con centration in fluoborate ions, and in vessels of plastic material (ebonite, polyethylene, polyvinyl chloride, polyester resin, etc.) or of sheet metal covered with plastic material when the baths employed have a higher concentration in fiuoborate ions. The bath can be heated either by immersion heater or by Water bath.

The metallic platinum which is deposited at the cathode is replaced by the addition of fresh bath. The level of the solution is maintained at its initial height by addition of distilled water or electrolyte if the need should arise.

By way of example, there will now be given below a few formulae of baths which have been employed, as

well as the operating conditions and the results obtained:

Formula 1 Platinum II diaminodinitrite 20 g./liter. Fluorboric acid 50 g./liter. Temperature 70 C. Current density 5 A/dm.

Thickness of metal deposited 6p. in 30 min.

Appearance of deposit High luster.

Formula 2 Platinum II diaminodinitrite 20 g./liter. Sodium fluoborate 100 g./liter. Temperature 75 C. Current density 7 A/dm Thickness of metal deposited 3.5;). in 30 min. Appearance of deposit Dull grey, free from internal stresses.

Formula 3 Platinum II diamiuodinitrite 20 g./ liter. Sodium fiuoborate 100 g./liter. Fluoboric acid l g./liter. Temperature 75 C. Current density 4 A/dm. Thickness of metal deposited p. in 30 min.

Appearance of deposit Bright luster, free from internal stresses at lO/u and upwards.

Current density l A/dm. Thickness of metal deposited Appearance of deposit 2a in 30 min. Bright luster, free from internal stresses.

The deposits noted above are obtained from any one of the baths highly adherent, both on brass or nickel and on copper, silver or gold. There are formed in a single operation layers having a thickness of 15a and upwards. The platinum content can be very low in view of the fact that the only eitect of a reduction in platinum content is a reduction in the rate of deposition, the appearance of the deposit being in no way modified.

It will naturally be understool that the invention is not limited in any respect to the examples of embodiment or modes of applications which have been more especially contemplated and is intended, on the contrary, to include within its scope all alternative forms.

What we claim is:

1. An aqueous acidic electrolytic bath for electroplating platinum consisting essentially of platinum II diaminodinitrite and at least one compound which provides sufficient fluoborate ions in solution to complex said platinum compound.

2. An electrolytic bath according to claim 1 wherein the compound which provides the fluoborate ions is selected from the group consisting of fluoboric acid, alkali metal fluoborate and ammonium fluoborate.

3. An electrolytic bath according to claim 1 wherein the platinum II diaminodinitrite is present in a concentration of from about 5 to at least 40 g./liter of solution and the compound which provides the fluoborate ions is present in a concentration of from about 20 to 200 g./'liter and is selected from the group consisting of alkali metal fluoborate and ammonuim fiuoborate.

4. An electrolytic bath according to claim 1 wherein fluoboric acid is the compound which yields the fiuoborate ion and said acid is present in a concentration of from 5 to g./liter of solution.

5. An electrolytic bath according to claim 3 wherein the compound which provides the fluoborate ions is selected from the group consisting of sodium fluoborate and potassium fluoborate.

6. An electrolytic bath according to claim 1 wherein the compound which provides the fluoborate ions is a mixture of fluoboric acid and an alkaline fluoborate salt selected from the group consisting of alkali metal fluoborate and ammonium fiuoborate and said fluoboric acid is present in a concentration of from about 5 to 100 g./liter of solution and said alkaline fluoborate salt is present in a concentration of from about 20 to 200 g./ liter of solution.

7. An aqueous acidic electrolytic bath for plating platinum consisting essentially of 20 g./liter of platinum II diaminodinitrite and 50 g./liter of fluoboric acid.

8. An aqueous acidic eletcrolytic bath for plating platinum consisting essentially of 20 g./liter of platinum II diaminodinitrite and 100 g./liter of sodium fiuoborate.

9. An aqueous acidic electrolytic bath for plating platinum consisting essentially of 20 g./liter of platinum II diaminodinitrite, 100 g./liter of sodium fluoborate and 10 g./liter of fluoboric acid.

10. An aqueous acidic electrolytic bath for plating platinum consisting essentially of 5 g./liter of platinum II diaminodinitrite, 50 g./liter sodium fluoborate and 10 g./ liter. fluoboric acid.

References Cited UNITED STATES PATENTS JOHN H. MACK, Primary Examiner.

G. KAPLAN, Assistant Examiner. 

1. AN AQUEOUS ACIDIC ELECTROLYTIC BATH FOR ELECTROPLATING PLATINUM CONSISTING ESSENTIALLY OF PLATINUM II DIAMINODINITRITE AND AT LEAST ONE COMPOUND WHICH PROVIDES SUFFICIENT FLUOBORATE IONS IN SOLUTION TO COMPLEX SAID PLATINUM COMPOUND. 